1. Field of the Invention
This invention relates generally to controllers for systems having periodic output functions with measurable parameters such as pressure, flow, motion, and the like, and more particularly relates to an electronically controlled ventilator system for providing respiratory gas to a patient, and an improved system and method for discrete time control of ventilation flow during patient breaths.
2. Description of Related Art
Breathing ventilator systems conventionally provide breathing gas to a patient for pressure supported breath assistance at a pressure support level as high as 70 centimeters of water, or minimal pressure, usually no more than 2 centimeters of water above baseline.
Conventional ventilators typically provide breath inhalation support at regular intervals, or at intervals triggered by a patient's spontaneous inspiration effort. Errors in the delivery of gas flow as compared to the desired gas flow at the appropriate time can occur due to lag time between the onset of patient inspiratory effort and actual valve response time, regulator response, and valve gain variations. Although typical flow controllers may utilize a feedforward flow control gain component and various types of feedback error correction, such as proportional, integral, or derivative error feedback control, to compensate for real time disturbances that occur in the system, such systems frequently have difficulty in correcting for any sustained errors that occur periodically in the system.
Until recently, such inaccuracy in flow control of ventilators has hampered application of ventilators for infant and neonatal patients. It would therefore be desirable to provide a system for adaptive response to periodic disturbances in a ventilator flow system, based upon past system performance with the correction including an integration of flow rate errors during all of the previous breath control intervals for a patient. It would be desirable for every control interval of patient assisted breathing to be affected by a correction component, so that the output flow rate matches the actual demands on the system.
A major factor in assisting patient breathing is the energy required by a patient to trigger and obtain an adequate flow of respiratory gas. It would therefore be desirable to improve the accuracy of flow control to reduce this energy requirement in the work of breathing.